A major problem in the distillation of seawater and brine, generated during the drilling of oil wells, is the formation of scale. The term "scaling" or "precipitation" as used herein, refers to the deposits which tend to form and build up on the heat exchange surfaces of vaporizing devices. Scale also becomes a particularly serious problem in salt concentrators, but is less serious in machinery intended only to take a small proportion of the water, rejecting a brine that is only slightly concentrated compared with the original input material. In every form of separation of salts from water, the problems multiply many fold when it is required to achieve a high degree of concentration of the solute materials.
The formation of scale causes a gradual reduction in the efficiency and rate of output of distillate. In thermal compression devices, an efficient apparatus for distilling seawater, scale formation not only decreases the output of the unit, but increases the horsepower necessary to drive the vapor compressor. The inefficiency caused by scaling greatly increases the cost of manufacturing distillate and therefore, it is customary to completely shut down the manufacturing process so that the scale can be removed from the heat exchange surfaces of the vaporizing device.
Even if efficiency is not the most important factor in a particular installation, frequent removal of scale is dictated because thick scale is more difficult to remove than thin scale. There is also a danger that thick particles of scale will flake off during operation of the distillation device and damage or cause undue wear to the apparatus. Conventional methods for removing scale include acid and chemical treatment in addition to ultrasonic vibrations. These methods are time consuming, costly and require lengthy shut downs of the distilling apparatus.
It is known that there are many factors which will influence the tendency and rate of scaling of the heat exchange surface by seawater or brine during the vaporization process. These factors include the retention time of the seawater within the vaporization chamber, the quantity of foreign matter in the seawater, the roughness of the heat exchange surface, the type of metal with which the seawater comes into contact within the distillation unit and the carbon dioxide equilibrium of the seawater. Solutions to the scaling problem have been proposed such as, for example, controlling certain operational conditions of the distillation apparatus. Such a proposal is described in U.S. Pat. No. 3,236,748 issued to Pottharst, Jr. on Feb. 22, 1966 and entitled "Process for Distilling Sea Water". However, such devices have required complicated structures and temperature monitoring devices to minimize scaling. Further, since the impurity of the brine which is to be distilled has a bearing on scaling, it is difficult to consistently control the operating parameters of the distillation apparatus.
An additional factor relating to the efficient operation of vapor compression distilling and concentrating devices is the presence of air in the incoming raw unconcentrated brine. The air dissolved in the raw brine results in continually increasing the concentration of air mixed with the generated vapor thus decreasing the efficient performance of the system.
A need has thus arisen for a vapor compression distilling and concentrating device which provides for easy removal of the heat exchange device so that the heat exchange surfaces can be readily cleaned of scale to avoid costly downtime of the distillation device. A need has further arisen for a distillation device which provides for the removal of dissolved air being carried into the system by the raw unconcentrated brine. A need has further arisen for a distillation device which is simple in operation to minimize the cost of manufacturing distillate and which provides for efficient concentrate disposal.